Dehydrogenation of alkyl pyridines including depolymerization of polymers



Aug. 15, 1961 URK ET AL Filed July 7. 1959 S. D. T DEHYDROGENATION OF ALKYL PYRIDINE DEPOLYMERIZATION OF' POLYM S INCLUDING ERS A TTORNEYS United States Patent 2,996,509 DEHYDROGENATION F ALKYL PYRIDINES IN- CLUDING DEPOLYMERIZATION 0F POLYMEBS Stanley D. Turk and Billy D. Simpson, Bartlesville,

Okla., assignors to Phillips Petroleum Company, a corporation of Delaware Filed July 7, 1959, Ser. No. 825,457 `6 Claims. (Cl. 2641-290) This invention relates to -a process for the production of heterocyclic nitrogen-containing bases of the pyridine, quinoline, and isoquinoline series and, more particularly, the invention relates to the depolymerization or pyrolysis of polymers of the polymerizable heterocyclic nitrogencontaining bases, such as polymers of 2-vinylpyridine and vinylquino1ine. In accordance with one aspect, this invention relates to a novel process for the production of pyridine, quinoline, and isoquinoline derivatives from polymers of alkenyl substituent pyridines, quinolines, and isoquinolines by pyrolysis. In accordance with another aspect, this invention relates to a depolymerization process for converting polymers having heterocyclic nitrogencontaining substituents to monomers. In accordance with another aspect, this invention relates to an improved process for the dehydrogenation of alkyl substituted heterocyclic nitrogen-containing compounds to alkenyl substituted heterocyclic nitrogen-containing compounds which form polymers during processing, said improvement comprising removing polymer formed during said dehydrogenation process, heating said polymer to an elevated temperature to convert the polymers to simple heterocyclic nitrogen base derivatives, and separating said derivatives, recovering the alkenyl substituted products, and returning dehydrogenatable derivatives to said dehydrogenation process to materially increase the yield of desired dehydrogenated heterocyclic nitrogen bases in said process.

The production of alkenylpyridines, especially vinylpyridines, has recently become of much industrial importance. Vinylpyridines can be prepared by condensation of formaldehyde with 2- and 4-methylpyridines or substituted derivatives to form the monomethylol compounds followed by dehydration of same to produce corresponding vinylpyridines or substituted Vinylpyridines.

A more direct procedure is the direct catalytic dehydrogenation of the dehydrogenatable alkylpyridines to the corresponding alkenylpyridines. Thus, for example, Z-methyl-S-ethylpyridine can be efficiently dehydrogenated to produ-ce the corresponding 2methyl5vinylpyridine. This can be done, for example, by passing an admixture of from 2 to 15 -Weights of steam per weight of 2-methyl S-ethylpyn'dne at a temperature within the range of 1,000 to 1,300 F., approximately atmospheric pressure, and a space velocity of 1 to 5 liquid volumes Z-methyl-S- ethylpyridine charge per volume of catalyst per hour, over a catalyst exemplied by one composed of 93 Weight percent iron oxide, 5 percent chromium oxide and 2 percent potassium hydroxide, as described and claimed in further detail in U.S. Patent 2,769,811 of John E. Mahan, issued November 6, 1956. The dehydrogenation euent contains, in addition to hydrogen, principally unchanged 2-methyl-5-ethylpyridine (MEP) and 2-methyl-5-vinylpyridine (MVP) product. Also present are small quantities of Pyridine 2-picoline 3-picoline 2,5-lutidine 3-ethylpyridine 3vinylpyridine.

Processing of Vinylpyridines contained in this or other ice mixtures presents many diiculties. These arise because of the great ease with which Vinylpyridines, in particular, polymerize. In fact, solutions containing these alkenyl bases frequently contain some polymer, since in the absence of highly effective inhibitor, the monomers polymerize under ordinary conditions of storage. For many uses, it is desirable to remove the polymer, and the recovered polymers represent by-products. In accordance with the present invention, We have discovered a new and valuable use for such polymers which comprises depolymerizing said polymers at an elevated temperature to form simple pyridine derivatives.

Accordingly, an object of this invention is to provide a process for the production of heterocyclic nitrogen bases of the pyridine, quinoline, and isoquinoline series. Another object of this invention is to provide a process for the depolymerization of polymers prepared from polymerizable heterocyclic nitrogen-containing bases, such as the Vinylpyridines and the vinylquinolines. Another object of 4this invention is to provide a process for the conversion of polymers of heterocyclic nitrogen-containing materials to valuable products. Still another object of this invention is to provide an improved dehydrogenation process which is more ecient wherein polymer byproduct from said process is converted to additional valuable products -for use in the process. Another object of this invention is to provide an improved process for the dehydrogenation of methylethylpyridne to methylvinylpyridine.

Other aspects, objects, and the several advantages of the invention are apparent from a study of the disclosure, the drawing and the appended claims.

In accordance with the present invention, a novel process is provided for the preparation of valuable products `from polymers of a polymerizable heterocyclic nitrogencontaining base which comprises heating a polymer of said vbase at an elevated temperature for a time suiicient to depolymerize said polymer to monomeric products and recovering said monomeric products as products of the process. We have discovered that, by subjecting a polymer of certain polymerizable heterocyclic nitrogen-containing bases to pyrolysis within a temperature range of about 250 to about 600 C., and preferably at subatmospheric pressure, substantially all of the polymer is converted into monomeric products.

More specifically, in accordance with the present invention, a novel proces is provided -for the production of heterocyclic nitrogen bases of the pyridine, quinoline, and isoquinoline series by pyrolysis which comprises heating a polymer of one of said bases to a temperature of about 250 to about 600 C., preferably at subatmospheric pressure, and for a time suicient to convert substantially all of said polymer to heterocyclic nitrogen Abases of the pyridine, quinoline, and isoquinoline series and recovering said bases as a product of the process.

In accordance with a specific embodiment of the present invention, an improved process for the dehydrogenation of alkylpyridines to alkenylpyridines is provided which comprises heating an alkylpyridine containing feed stream, separating polymer from said heated stream,subjecting said alkylpyridine to dehydrogenation, separating said dehydrogenation effluent into an alkenylpyridine product, unreacted alkylpyridine recycle, and additional polymer, combining said separated polymer streams and heating the polymer to a temperature Within the range of about 250 to about 600 C. at subatmospheric pressure to convert said polymer to alkyl and alkenyl substituted pyridines, and recovering said alkyl and alkenyl pyridines as products of the process, thereby materially increasing the yield of desired dehydrogenaied pyridine.

Polymeric materials which can be advantageouslylprocessed, according to the praoticeof the presentY invention,

comprise the liquid and solidY polymers of one or more polymerizable monomers of=the heterocyclic nitrogen bases of-'the pyridine, quinoline; and .-isoquinolineseries represented by thestructural formulas- R l Rf.

wherein'R'l is selectedfrom the vgroup -consistingjof hydrogen,` alkyl, Vinyl, and alphaamethylvinylf groups; and 'i wherein at least one of said groups` being vinyl and alphamethylvinyl, and the total number of carbon atoms Ainthe alkyl groups ldoes not exceed-`f12 Various alkyl-substituted derivatives `are also thefprecursors of these poly-` mers,YV and for these thev number ofy fcarboneatomsl'is Vnot greater than 12 Aand,lmost frequently,A are methyl and/ or ethyl groups.

The heterocyclic nitrogenbasesof-thepyridine, quino ljne,-and isoquinoline series obtained as products,'accord ing tothe Vpractice of our invention; -will'be determined by' the nature of the startingfpolymeric material; Typical liquidv and `solid 'polymers off-the ytype -described'l above which'can be .advantageouslyprocessed, according to` this invention; include polymers of one ormorefof the followr-v f ing monomers.

and the like.

The .reaction temperature for lthe presentzprocess 4'will usually be in therange romxaboutZSO to 600 C." The'` rate of depolymerization of the rpolymerstreatedv according Lto-.the present inventionfvaries directly withlthetemperature.

period is requiredthan.atthehighertemperaturesffor ex-A ample, 500 -to 6007 C. Thertotal reactiontperiodlofthe. present process will be: Vin 'the rangeffrom'about v0.0110- about 100 hours. Pyrolysis of the polymerickmaterial is preferably eieoted under subatmospheric pressure',. that is-,a at pressures below 1 atmosphere, suchas pressures vof the: order of 1 mm. Hg, Vor lower, so as to facilitatelrapidJe-L moval of the. volatile products from the depolymerization' zone. However, if desiredatmospheric andfhigherpressures, for example,- pressures:of= lfatmospheres and such as steam or nitrogen.,

Polymer-ic materials .Whichfcanube depolymerized, .,ao cording tothe practice ofthe presentinventiomantbe.. passed to the depolymerization zoneLmixed withfay suitable diluent or solvent; Suitable diluents' or solvents'incliidegt and monomeric vinylpyridines and-theh alkylvinylpyridines.

Dil-uentsv or solventsemployed-- are Apreferably vmaterials Therefore,; tof. obtain complete or-essential-ly complete '.depolymerization ofthe .materials atr lower--ternperatures, for example, 250 to.400. C., a longerftheating 2,996,509. i f e higher pressures can be employed.;` The volatile-products: in the depolymerization; none. can Ifbe, if desir-ed; swept: from the depolymerization .zoneby the use-of aninert gas,1

that can be readily separated from the viuyl-pyridines produced in the depolymerizationzone by distillation. For example, 2-methyl-5-ethylpyridine can be advantageously employed.

A better understandingzof tthisr invention willl be obtainedby reference to theraocompanying drawing .vvlitereiriu4 polymers formed in the-process of p reparingmethylvinyl pyridine from methylethylpyridine are passedtoa-depoly-M merization zoneand converted lto additional pyridines for use in the dehydrogenation process.

Referring now'to the-drawing, a Vfeed stream comprising 2-methyl-5-ethylpyridine (MEP) is passed to surge tanktl() byyway of conduit-11.r Recyclel/IEP- is introducedinto-surge tank 10'by Way vofconduit-IZ.Y The` MEPffeedie-removed fromfsurge'tank 10s by Yway of conduit-13 and passed to furnace :14 wherein it is heated to a temperature 'of-about `70h C. The heated feed-.isremoved fromV lfurnace A14 -by -Way `of-conduit A15 Y andintroduced intotilashfzone- IG-.Wherein A.vaporized MEP is removed overhead through `conduit- 17. A high boiling r liquidy andsolid polymer mixture, such as resulting from Y the- 'thermal' Vpolymerization 4of V2-.methyl-5 -viuylpyridine and S-Vinylpyridine, is removed from ash zonet16 by-way ofconduitzlS.'

. The Ahigh boiling mixture-removed from ash zone-16 by Way Tof .conduit- IS is introduced .into steam stripping zone.-19 wherein MEP is` removed overhead by -waytof conduita'Z-andrmixed with-MEP in conduit '17. Steam is introduced-into ythe ibase of-zone-19 by conduit 21. Stripped-.polymers are removed fromthe-base of zone 19 byywayfof` conduit 22 -for'rfuxther processingto' be describedmereinaftr.' Vaporized MEPremoved from zone 16andzone 19 ata-temperature of about 270 C. and abouts30-p.s.i.a..is admixed with superheated steam in conduit- 23.Y Superheated steam is introduced byway of eonduit24 in a ratio `ofabout. 3.5 :1 to about 7 .0:1 pounds oft-steamrper .pound of MEP. Steamintroduced by way` of-conduit 24 issuiciently superheated'that the feed mixture -passedato dehydrogenation zoneZS is at atemperature of about 650 C.

. In 'zone Zia-MEP is-dehydrogenated-to MVP' preferably inthe presence offa catalyst which contains-93Weight percent Fe203, -5 `Weight* percent CrZOa` and 2 percent KOH.- Pressures lemployedin zone 25 are-generally `inthe range' of-l00 mmxmercury pressure absolute to^25 p.s.i.g. The owrates-in-zone 25 range from 0.2 to-S liquid-volumes pyridinefztcharge per volume -ofcatalyst lper hour,` which corresponds to approximately 35 to 850 volumes gaseous alkylpyridine- (calculated at standard` Vtemperature and pressure` pervolume :of catalyst 'per hour) The effluentfromdehydrogenation zone 25 is removed by Wayv of'conduit-26 and cooled to about 200 C. in heat exchangerZZ, and thenvquenched to about 65 C. in'zone 2,8.. A quenching medium is introduced linto zone Z8 lby Way vof conduit 29s The .cooled and liquefied'dehydrogenation eiuentfremovedffromrzone 28is -passed by 4Way of conduit 30 to phase separator 2:1.V In phase separator 31,.the.mixture is `separated into-an aqueous and organic p hase, the aqueous phase being removed by way of conduit 32.@ Oi gascompn'sing mainly hydrogen and other inert gases .isgremovedfrom separator 31 by vway of conduit 33.

Theorganic phase separated in separator 31 is vpassed to Y surge tankSS byway of pipe 34. A mixture ofpredominantlyMEP andMVRis lpassed through line-37 to fracn'onation column $8. The latter may be-,of'any eonven-Y tionaltype capable. of providing countercurrent contact of liquid and vapors with reflux. Superheated steam can be injected into the base of fractionation zone 38 by Way of line 39.

Overhead vapors removedrfromlone 38 consisting of steam yand organic vapors predominantly MEP by conduit 40 are condensed in condenserALand separated into an aqueous and organic phaseaaccurnulator 4Z. The water phase isV removed from accumulator 4Z by conduit 43. Tlieorganic layerwitlrdrawn through conduit'44 and essere@ t? d divided into two streams, one portion being Withdrawn through conduit 4S for MEP recovery, the other recycled through conduit 46 to fractionator 38 as reliux. Sulfur, not shown, can be added to the reflux as a polymerization inhibitor. 'Ihe organic layer removed by conduit 4S is passed to fractionator 47 for separation into an overhead vinylpyridine stream, removed by conduit 48 and a bottoms MEP stream removed by conduit 12 and recycled to surge tank 10.

MVP and polymer-ized vinylpyridine and higher-boiling residual materials are removed from the base of fractionation zone 38 by conduit 50 and passed to flash zone 51. MVP product is removed from the top of zone 51 by way of conduit 52. Polymers of vinylpyridines and higherboiling residual materials are removed from the base of ash zone 51 by conduit 53.

In accordance with the present invention, the polymers removed from the dehydrogenation process by conduits 22 and 53 are introduced into conduit 54, mixed with a suitable dluent, such as MEP, introduced by way of conduit 55 and passed to depolymerization zone 56. In depolymerization zone 56, the polymeric feed mixture is heated to a temperature withinthe range of about 250 to about 600 C., preferably at subatmospheric pressure, for suicient time to depolymerize substantially all of said polymers and forma mixture of pyridine derivatives comprising S-ethylpyridine, 2-picoline, 2,5-lutidine, MVP, MEP, and 3-vinylpyridine. The depolymerization' zone eiuent mixture of pyridine derivatives is moved from zone 56 by way of conduit 57 and passed preferably to separation zone 58 which can comprise a plurality of separation zones including fractionation, solvent extraction, and the like.

The pyridine derivative mixture obtained as depolymerization zone effluent passed to zone S8 is perferably separated into a plurality of individual component streams. MEP is removed from separation zone 58 by pipe 60 and passed to pipe 12 for recycle to dehydrogenation Zone 25 along with MEP recovered from zone 47. MVP is removed from zone 58 by pipe 61 and combined With MVP in pipe 52 recovered from zone 51, thereby materially increasing the yield of dehydrogenated pyridine product recovered from the process. Other depolymerization products recovered 4from zone 58 include 3-ethylpyridine removed by pipe 62, 3vinylpyridine removed by pipe 63, and 2-picoline `and 2,5-lutidine removed by way of pipe 64'. These products can be combined with the same products recovered from the dehydrogenation eluent or passed to separate places of separation or utilization, not shown. Diluent and polymeric material can be removed from zone 58 and recycled to zone 56 by way of conduit 59.

By operating according to the practice of the present invention, polymers present in the feed to a dehydrogenatable alkylpyridine dehydrogenator rare advantageously separated prior to dehydrogenation. These polymers as well as polymers formed during and after dehydrogenation are depolymerized, as above described, and the products obtained are preferably combined with the same materials recovered from the dehydrogenatio'n eiliuent. Also by operation according to the present invention, the alkenylpyridines from the depolymerization zone products are recovered without passing these materials through the dehydrogenatio'n zone a second time thereby increasing the throughput capacity of the dehydrogenator. Further, by depolymerizing polymers, according to the practice of the present invention, as herein disclosed, there results an increase in the ultimate yield of the desired alkenylpyridine. Furthermore, the vinylpyridines resulting from the thermal depolymerizatio'n of the polymers are recovered without need for modiiication of the dehydrogenation process. Clearly, it can be seen that only the dehydrogenatable alkylpyridines are recycled through the dehydrogenation zone, as discussed above.

The following example will serve to illustrate the ad- 6 vantages orf-my invention and should not be construed to limit the invention unduly.

EXAM PLE For this example, a kettle product, representing a polymer stream, such as removed by pipe 22 of the accompanying drawing, was employed. This kettle product comprises polymer contained in the 2-methyl-5-ethylpyridine stream which has been heated in zone 14 and arise principally `from. polymerization of Z-methyl-S-vinylpyridine and 3-vinylpyridine. This product was found to contain about 32 percent water and 3 percent volatile pyridines as determined by heating to C. under high vacuum (less than 1 mm. mercury pressure) until no loss in weight occurred. The remainder, about 65 percent, represented high boiling polymers.

The kettle product described above was depolymerized by heating -in a 32 mm. Pyrex tube which was 25 inches long. 'Ihe tube was heated by two tube furnaces. Three thermocouples were spaced equally apart within the tube for measurement of the temperature. The tube was inclined slightly. The kettle product was diluted with 10 weight percent methylethylpyridine (Ibased on polymer) and fed slowly into the tube which was initially preheated to a temperature between 262 and 496 C. while keeping the pressure between 10-19 mm. of mercury. The liquid products owed from the tube into a flask; and volatile gases passed through a condenser connected to a second flask. Vapors not condensed in this second ask were passed through a Dry Ice trap. These condensed products were com'bined, and then flash distilled at 10 mercury pressure. 'Ihe maximum boiling point of the material which was distilled was 65 C. These products were analyzed.

Table Run! A Bs 2,5-lntdino 2-methy1-5-ethylpy1idiue (MEP) 3-vinylpyridine (BVP) 2-methyl-5-vinylpyridiue (MVP) 1 These were runs in which the feed was continuously added t0 the pyrolysis tube.

2 Corrected for MEP added 1and volatile pyridines present in steam-stripper kettle produc B'Based on 65 per cent dry polymer present in the steamstripper kettle product fed.

*.Corrected for the MEP originally present in the steamstripper kettle product and that which was added.

5Onrecycle of the nou-volatile material from Run B, approximately 13 percent was cracked to give a pyrolysate conta1mng 61.7 percent 3-vinylpyridine and 25.9l percent 2- methyl--vrnylpyridine.

This table summarizes the pertinent data from two runs. These data show that 48.7 and 51.1 percent by weight of the polymer in the kettle product was cracked and recovered as volatile pyridines. -For these runs, this pyridine fraction was found to comprise 64.0-65 .3 percent by weight of 3-vnylpyridine and 21.6-23.1 percent by weight of 2-methyl-5-vinylpyridine. 'Ihe alkylpyridines, principally 2-methyl-5-ethylpyridine, amount to l3.0-13.3 percent by weight of the cracked material. Thus, by depolymerizing the polymeric residue and recovering the volatile pyridines, as herein disclosed, there results an increase in the ultimate yield of the desired alkenylpyridine. Further, the vinylpyridines resulting from the thermalv depolymerization of the polymer `is recovered without need for mo'diiication of the process. Only the 'alkylpyridines are recycled through the dehydrogenation zone.

Reasonable variation and modification are possible within the scope of the foregoing disclosure, the drawing, and the appended claimsto be invention, the essence of which is that an improved process has been provided for the production of 4aliphatic: substituted pyridine, quinoliri'e, and isoquinoline components -by depolymerization which comprises heating a polymer formed by polymerization of a polymerizable vinylpyridine, vinylquinoline, and vinylisoquinoline mixed with a diluent or solvent, if desired, to an elevated temperature, such as a temperature within the range of about 250 to about 600 C., preferably at subatmospheric pressure, and for a time sufficient to convert substantially all of said polymer to heterocyclic nitrogen bases of the pyridine, quinoline, and isoquinoline series and recovering said bases as products of the process.

We claim:

1. An improved process for the conversion of 2-methyl- 5-ethylpyridine to Z-methyl-S-vinylpyridine by dehydrogenation which comprises heating said Z-methyl-S-ethylpyridine, separating polymeric materials from said heated Z-methyl-S-ethylpyridine, dehydrogenating said Z-methyl- S-ethylpyridine to 2-methyl-5-vinylpyridine, separating the dehydrogenation eiuent into a vinylpyridine product, a Z-methyl-S-ethylpyridine recycle stream, and a Z-methyl- 5-vinylpyridine product, and separating polymeric materials present in said effluent, the improvement comprising passing said separated polymeric material to a depolymerization zone, heating said polymers to a temperature in the range of about 250 to about 600 C. at subatmospheric pressure in said depolymerization zone for a suiicient time to convert substantially all of said polymer lto simple pyridine derivatives, separating the various derivatives from said depolymerization zone eiuent, recovering the alkenyl substituted products, returning dehydrogenatable pyridines to the dehydrogenation zone, land returning diluent and polymeric material to said depolyrnerization zone.

2. An improved process for the dehydrogenation of Valkylpyridines toalkenylpyridines comprising heating a feed stream containing said alkyl pyridines, separating polymeric materials present in said feed stream from said feed stream, dehydrogenating the remainder of said feed stream in a first zone, passing the rthus separated polymeric materials to a second-zone, the feed to said second zone consisting essentially of polymeric materials, subjecting said polymeric materials to an elevated temperature in said second zone for a sutlicient time to convert substantially al1 of said polymeric materials to monomeric products, converting substantially all of said polymeric materials in said second zone to monomeric products, and recovering said monomeric products thus produced. Y

3. An improved process for the dehydrogenation of alkylpyridines to allrenylpyridines,comprising'heating a feed stream containing said alkyl pyridines, separating polymeric materials present :in said feed stream from said feed stream, dehydrogenating the remainder of said feed stream in a rst zone, separating polymericmaterials from the dehydrogenation effluent, separating said dehydrogenation eiuent into an alkenylpyridine product and an alkylpynidine recycle stream, passing the thus separated polymeric materials to a secondzone, the feed to said second zone consisting essentially of polymeric materials, subjecting said polymeric materials to an elevated temperature in said second zone for a suicient time to convert substantially all of said polymeric materials to monomeric products, converting substantially all of said polymeric materials in said second zone to monomeric products, separating the various monomeric products from the eluent from said second zone, recovering the alkenyl substituted products, returning dehydrogenatable pyridines to said iirst zone, .and returning polymeric materials to said second zone.

4. A process according to claim 2 wherein said elevated temperature is in `the range of about 250 C. to about 600 C. v

5. A process according to claim 2 wherein said alkyl pyridine is 2methyl5ethylpyridine and said alkenyl pyridine is 2-methy1-5-viny1pyridine. A 6. An improved process for the dehydrogenation of alkyl pyridines to alkenyl pyridines comprising heating a feed stream containing said alkyl pyridines in a iirst zone, dehydrogenating the heated feed stream in a second zone, separating polymeric materials from the dehydrogenation euent, passing the thus separated polymeric materials to `a third zone, the feed to said zone consisting essentially of polymeric materials, subjecting said poly-v meric materials to an elevated temperature in said third zone for a sufhcient time to convert substantially all of said polymeric materials to monomeric products, converting substantially all of said polymeric materials in said third zone to monomeric products, separating the various monomeric products from the effluent from said third zone, recovering the alkenyl substituted products, and returning only dehydrogenatable pyridines to said second zone. v

Hurd: Pyrolysis of Carbon Compounds, pp. 745-748 (192.9), (Chem. Catalog Co.).

UNITED STATES. PATENTOFFICE CERTIFICATE OF CORRECT-IGN 's Patent No.v 2,996,509v August 15, 1961-;l

v corrected below.

Stanley D. Turk et al.

. It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent ehouldread as Column 7, line 32, for ."polymers" read polymeric material lines 35 and 36, for "polymer read polymeric material VSigned andsealed this 20th day of February 1962.

(SEAL) l Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer t A. Commissioner of lPatents 

2. AN IMPROVED PROCESS FOR THE DEHYDROGENATION OF ALKYLPHRIDINES TO ALKENYLPHYRIDINES COMPRISING HEATING A FEED STREAM CONTAINING SAID ALKYL PYRIDINES, SEPARATING POLYMERIC MATERIALS PRESENT IN SAID FEED STREAM FROM SAID FEED STREAM, DEHYDROGENATING THE REMAINDER OF SAID FEED STREAM IN A FIRST ZONE, PASSING THE THUS SEPARATED POLYMERIC MATERIALS TO A SECOND ZONE, THE FEED TO SAID SECOND ZONE CONSISTING ESSENTIALLY OF POLYMERIC MATERIALS SUBJECTING SAID POLYMERIC MATERIALS TO AN ELEVATED TEMPERATURE IN SAID SECOND ZONE FOR A SUFFICIENT TIME TO CONVERT SUBSTANTIALLY ALL OF SAID POLYMERIC MATERIALS TO MONOMERIC PRODUCTS, CONVERTING SUBSTANTIALLY ALL OF SAID POLYMERIC MATERIALS IN SAID SECOND ZONE TO MONOMERIC PRODUCTS, AND RECOVERING SAID MONOMERIC PRODUCTS THUS PRODUCED. 